She’s just become the youngest player to earn $US1 million ($A1.1 million) on the LPGA circuit, but 17-year-old golfer Lydia Ko still gets a kick out of every boost to her pocket money.

The Aucklander calmly birdied her final hole on Sunday to nail a come-from-behind win in the Marathon Classic in Ohio. Her 15-under gave her a one-shot win over South Korea’s fast-finishing So Yeon Ryu.

Ko’s winning purse of $US210,000 made her the youngest LPGA player to reach $US1m in prize money, a record previously held by American Lexi Thompson, who was 18 at the time.

Ko wasn’t aware she was youngest LPGA millionaire until informed during media interviews after her win.

“I am pretty sure that goes into my mom’s account or something,” she said.

Ko admitted she gets an extra $10 in pocket money for each shot under par she finishes, which prompted laughter from reporters.

“It’s good, I mean, to me that’s kind of more fun, thinking about pocket money and getting money off your mom, that’s exciting for me.

“I’m not going to spend a million dollars on something like buying a diamond ring … Maybe I might get something electronic.”

Ko started the fourth and final round in fifth place, two shots off the pace, but quickly made up the difference with birdies on the third and fourth holes.

As overnight leaders Le-Anne Pace and Laura Diaz faded, Ko’s main challenges came from 36-year-old American Cristie Kerr, who started a shot behind Ko, and Ryu.

Ryu had shot a birdie on the 17th hole, which prompted Ko’s birdie reply on the par-5 18th, with the four-foot putt in the “nerve-wracking range”.

Ko couldn’t see Ryu’s putt to force a playoff, because she was behind people, but knew by the crowd’s reaction she had missed.

“Every shot makes me nervous, coming down the stretch makes me nervous. I think through experience I think I’ll be able to cope with that,” Ko said.

Ohio was Ko’s fourth win on the LPGA Tour. It is not enough for her to become the World No.1 but it will close the sizeable gap between her and American Stacey Lewis.

Australia’s Katherine Kirk hit a final-round 68 to tie for fourth at 11 under with Malaysia’s Kelly Tan.

Ko’s victory is also likely to have all but secured the LPGA Tour Rookie of the Year honours as she has recorded seven top-five finishes.

She now takes a two-week break before her next tournament.